1. Field of the Invention
The present invention relates to a method and system for estimating an inertia of torsionally vibrating 2-mass system in a speed control.
2. Description of the Prior Art
It is well known that if 2-mass system is constituted by a motor and a load connected through a low rigidity shaft (elastic shaft) in an elevator, rolling mill of steel or arm of robot, the 2-mass system generates a shaft torsional vibration and cannot be improved in responsibility of a speed control system. Further, such a shaft torsional vibration is effected by a ratio between inertia of moments of the motor and the load. In particular, the vibration tends to be generated when the moment of inertia of the load is smaller than that of the motor. Although a conventional method, which uses a load torque estimating observer, has been proposed for the control of the 2-mass system, the method is not very effective for suppressing the shaft torsional vibration when the moment of inertia of the load is smaller than that of the motor.
Furthermore, in order to effectively suppress the torsional vibration of the 2-mass system, a method for estimating inertia of the 2-mass system has been proposed. In this method, first, an inertia of 1-mass system (a motor) is estimated by a speed-accelerating test of a motor. Then, after the connection of a load with the motor, the 2-mass system is gradually accelerated so as not to generate a vibration, and under this condition an inertia of the 2-mass (motor+load) system is estimated.
However, such a conventional estimating method is not useful in a system which is applied to a condition that a load inertia is deviated during operation, such as, to a robot arm or an elevator since the conventional estimating method cannot implement the estimation of the 2-mass system which generates a torsional vibration during operation.